The camshaft position (CMP) actuator system enables the powertrain control module (PCM) to change camshaft timing while the engine is running. The CMP actuator assembly (5) varies camshaft position in response to directional changes in oil pressure. The CMP actuator solenoid valve controls the oil pressure that is applied to advance or retard the camshaft. Modifying camshaft timing under changing engine demand provides better balance between the following performance concerns:
The CMP actuator solenoid valve (3) is controlled by the PCM. The crankshaft position (CKP) sensor (4) and the CMP sensor (1) are used to monitor changes in camshaft position. The PCM uses information from the following sensors in order to calculate the desired camshaft position:
The CMP actuator assembly has an outer housing that is driven by the engine timing chain. Inside the assembly is a wheel with fixed vanes that is attached to the intake camshaft. Oil pressure that is applied to the advance side of the fixed vanes will rotate the camshaft in a clockwise direction. The clockwise movement of the camshaft will advance the timing up to a maximum of 21 degrees. When oil pressure is applied to the return side of the vanes, the camshaft will rotate counterclockwise until returning to 0 degrees. The CMP actuator solenoid valve directs the oil flow that controls the camshaft movement. The PCM commands the CMP solenoid to move the solenoid plunger (2) and spool valve (1) until oil flows from the advance passage (7). Oil flowing thru the CMP actuator assembly from the CMP solenoid advance passage applies pressure to the advance side of the vanes in the CMP actuator assembly. When the camshaft position is retarded, the CMP actuator solenoid valve directs oil to flow into the CMP actuator assembly from the retard passage (8). The PCM can also command the CMP actuator solenoid valve to stop oil flow from both passages in order to hold the current camshaft position.
The PCM operates the CMP actuator solenoid valve by pulse width modulation (PWM) of the solenoid coil (3). The higher the PWM duty cycle, the larger the change in camshaft timing. The CMP actuator assembly also contains a lock pin that prevents movement between the outer housing and the wheel vane assembly. The lock pin is released by oil pressure before any movement in the CMP actuator assembly takes place. The PCM is continuously comparing CMP sensor input with CKP sensor input in order to monitor camshaft position and detect any system malfunctions.
Driving Condition
Change in Camshaft Position
Objective
Result
Idle
No Change
Minimize Valve Overlap
Stabilize Idle Speed
Light Engine Load
Retard Valve Timing
Decrease Valve Overlap
Stable Engine Output
Medium Engine Load
Advance Valve Timing
Increase Valve Overlap
Better Fuel Economy with Lower Emissions
Low to Medium RPM with Heavy Load
Advance Intake Valve Closing
Improve Low to Mid-range Torque
High RPM with Heavy Load
Retard Intake Valve Closing
Improve Engine Output
